1. Field of the Invention
The present invention relates to a printer for performing printing of various types of information on a thermal paper drawn from a roll sheet.
2. Description of the Related Art
A large number of thermal printers of various types are presently provided in which printing is performed by pressing a thermal head against a special thermal paper (heat sensitive sheet) which undergoes a color change when heat is applied thereto. In particular, the thermal printer is suitably used in printing a variety of labels, receipts, and tickets because it is possible to perform the printing of smooth letters and various graphics without using toners, inks, or the like.
The above-mentioned thermal printer performs printing by sandwiching a thermal paper between a platen roller and a thermal head, and by heating a printing surface (heat sensitive surface) of the thermal paper by heating elements of the thermal head while feeding the thermal paper through rotation of the platen roller, thereby causing a color development of the printing surface. The thermal paper used in the thermal printer is a roll sheet type thermal paper in many cases, which is rolled in a roll shape. Roll sheets of several types each having a different width (for example, 3-inch width, 4-inch width, and so on) are provided, and used while appropriately selected according to the application.
Moreover, for the above-mentioned thermal printer, there is a demand for a single thermal printer that selectively performs printing on roll sheets each having a different width according to the printing purposes and applications.
However, in a conventional configuration, in a case of using a roll sheet having a smaller width (hereinafter, referred to as second roll sheet) than that of a roll sheet having a maximum usable width (hereinafter, referred to as first roll sheet), between the thermal head and the platen roller, on a widthwise outer side of the second roll sheet, a contact region is present in which the thermal paper does not pass through and the thermal head and the platen roller are brought into direct contact with each other. In the contact region, abrasion between the thermal head and the platen roller may cause a reduction of a feeding force due to a worn surface of the platen roller, damage of a protective film on the surface of the thermal head, and the like.
In this context, it is conceivable that platen rollers respectively corresponding to the widths of the roll sheets are prepared, and only the sizes of the platen rollers are changed according to size changes of the roll sheets. However, this configuration leads to a problem of an increase in cost of the apparatus.
Accordingly, for example, there is known the following configuration described in JP 2007-168350 A. Specifically, an application point of a resultant force of pressing forces, which are imparted to the thermal paper (platen roller) by the head springs supporting the thermal head, is set between a first center being a widthwise center of the first roll sheet, and a second center being a widthwise center of the second roll sheet.
However, the above-mentioned configuration of JP 2007-168350 A has a problem that, in a case of using the second roll sheet, the pressing force imparted to the contact region between the thermal head and the platen roller cannot be reduced yet fully.